In some embodiments, a transmitter transmits a packet comprising symbols over a channel to a receiver. The symbols are modulated according to the data they carry, such that symbols carrying different data types may be modulated with different modulations. The different modulations used for successive symbols within the same packet are selected from a subset of the same symbol set, or at least from partially overlapping subsets of the same symbol set. For example, a single packet may include X symbols modulated using PAM4, then Y symbols modulated using PAM8, then Z symbols modulated using PAM16, and then again X symbols modulated using PAM4. As a result, in order to decode the transmission properly, the receiver should determine the proper modulation for decoding each symbol or set of symbols. Referring to the last example, the receiver should demodulate the first X symbols using a PAM4 slicer, then demodulate the next Y symbols using a PAM8 slicer, then demodulate the next Z symbols using a PAM16 slicer, and then demodulate the last X symbols using the PAM4 slicer.
Different modulations for successive symbols within the same packet that are selected from subsets of the same symbol set, or at least from partially overlapping subsets of the same symbol set, are discussed in US patent publication number 2009/0115911 to Lida et al, entitled “methods for transmitting digital multimedia and data over the same wires”, which is incorporated herein by reference in its entirety. Therefore, the PAM4, PAM8, and PAM16 modulations used in the last example are modified PAM modulations having overlapping amplitude levels.
As explain above, in order for the receiver to properly decode symbols of different modulations within the same packet, the receiver should know the symbol's modulation and select the proper slicer. However, there are embodiments where at least some of the symbols' modulations are unknown to the receiver before slicing the symbols, and thus one or more of the methods discussed below are utilized to improve the receiver's performance.